frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/app/register/page.tsx

@@ -1,18 +1,5 @@
-"use client";
-
-import { useEffect } from "react";
-import { useRouter } from "next/navigation";
+import { redirect } from "next/navigation";
 
 export default function RegisterPage() {
-  const router = useRouter();
-
-  useEffect(() => {
-    router.replace("/");
-  }, [router]);
-
-  return (
-    <div className="flex min-h-screen items-center justify-center">
-      加载中...
-    </div>
-  );
+  redirect("/");
 }